1. Field of the Invention
This invention relates to a semiconductor laser device, and more particularly to a coupled-multiple-stripe semiconductor laser device which can produce a laser beam of high power.
2. DESCRIPTION OF THE PRIOR ART
Recently, semiconductor lasers including double heterostructures have become capable of continuous oscillations at the room temperature. A typical double heterostructure is constructed of n-type (GaA1As/p-type GaAs/p-type GaA1As.
The general construction of the semiconductor laser device of this type is as follows. On a p-GaAs (100) wafer substrate, there are successively stacked the compound semiconductor layers of a buffer layer (also termed "clad layer") of p-GaA1As which is formed by the liquid epitaxial growth, an active layer of GaAs (or GaA1As) which is formed on the buffer layer, and a clad layer of n-GaA1As which is formed on the active layer. Further, an upper evaporated metal electrode is formed through an SiO.sub.2 coating film having a strip-shaped opening, while a lower evaporated metal electrode is formed on the rear surface of the substrate. Thus, the semiconductor laser element having the stripe-geometry electrode is constructed.
In the semiconductor laser of this type, it has been proposed to increase the optical output of the whole device by juxtaposing a plurality of stripe light-emitting portions. An example is described in `Appl. Phys. Lett.`, vol. 34, No. 2, 15 January 1979, pp 162-165. In actuality, however, the respective stripes differ in the mode, wavelength and phase of laser radiation, and a laser beam of a quality high enough to be used for optical communication or in an optical disk memory, a laser beam printer etc. has not been obtained yet.
In this regard, when the intervals of the stripe electrodes are narrowed, the spreading width of current becomes greater than the light distribution width of a resonant laser beam (a laser beam oscillatingly reciprocating between both the optically flat faces of the crystal). Therefore, the current distribution becomes uniform before the light distribution does, and eventually the stripe electrodes act like a single electrode plate. In such case, the resonant laser beam gives rise to a filamentary oscillation irrespective of the stripe geometry, resulting in the disadvantage that light is emitted in the form of spots at random to drastically degrade the quality of the laser beam.